1. Field of the Invention
The present invention relates to wireless communications and, more particularly, to distribution of call load among coverage areas in a cellular wireless communication system.
2. Description of Related Art
In a typical cellular wireless communication system, an area is divided geographically into a number of cell sites, each defined by a radio frequency (RF) radiation pattern from a respective base transceiver station (BTS) antenna. The base station antennae in the cells are in turn coupled with a base station controller (BSC), which is then coupled with a switch or gateway that provides connectivity with a transport network such as the public switched telephone network (PSTN) or the Internet. For instance, the BSC may be coupled with a mobile switching center (MSC) that provides connectivity with the PSTN and/or the BSC may be coupled with a packet gateway, such as a packet data serving node (PDSN) or media gateway (MG), that provides connectivity with the Internet.
When a wireless communication device (WCD), such as a cellular telephone, pager, or wirelessly-equipped computer) is positioned in a cell, the WCD communicates via an RF air interface with the BTS antennae of a cell. Consequently, a communication path can be established between the WCD and the transport network, via the air interface, the BTS, the BSC and the switch or gateway.
With the explosive growth in demand for wireless communications, the level of call traffic in most cell sites has increased drastically over recent years. To help manage the call traffic, most cells in a wireless network are usually further divided into a number of sectors or other coverage areas, each defined respectively by radiation patterns from directional antenna components of the respective BTS, or by respective BTS antennae.
Further, in most wireless communication systems, multiple BTSs are connected with a common BSC, and multiple BSCs are connected with a common switch or gateway. Each BSC may then manage air interface resources for multiple wireless coverage areas (e.g., multiple cells and sectors), by performing functions such as assigning air interface traffic channels for use by WCDs in the coverage areas, controlling the power levels used for air interface communications, and orchestrating handoff of calls between coverage areas. And the switch and/or gateway, in turn, may control one or more BSCs and generally control wireless communications, by performing functions such receiving and processing call requests, instructing BSCs when to assign traffic channels, paging WCDs, and managing handoff of calls between BSCs.
The combination of network entities that provides a connection between WCDs and transport networks is considered a “radio access network” (RAN). In the arrangement described above, for instance, a RAN may include one or more BTSs, one or more BSCs, and an MSC. Of course, those skilled in the art will appreciate that these RAN entities are functional in nature and can therefore be combined or distributed in various ways. For example, BTS and BSC functions can be integrated together, and BSC and MSC functions can be integrated together. Further, a RAN can include other entities or take other forms altogether.
When a typical WCD powers on or otherwise enters the coverage of a given RAN, the WCD may register with the RAN and may then place and receive calls via the RAN. For instance, depending on the arrangement of the WCD, it may be able to place or receive voice calls, fax calls, and/or data calls (e.g., packet-data sessions) via the RAN. (Other WCDs may have more restricted functionality, such as being able to place but not receive calls, or vice versa.)
To initiate a call, when operating in a given sector or other coverage area of the RAN, for instance, the WCD may send an origination request into the RAN via an air interface access channel defined in the WCD's current sector. In response, the RAN may then assign an air interface traffic channel to be used for the call in the WCD's current sector, and the RAN may work to set up the call for the WCD. Upon successful connection, the call can commence.
On the other hand, when the RAN receives a request to connect a call to a particular WCD, the RAN may page the WCD via an air interface paging channel. When the WCD responds to the page, the RAN may then assign an air interface traffic channel to be used for the call in the WCD's current sector, and the call may commence.
Further, a RAN may facilitate handoff of an ongoing call from one wireless coverage area to another, such as from one sector to another. For example, while a WCD is engaged in a call, the WCD may regularly monitor received signal strength in its current sector and in neighboring sectors, and the WCD may notify the RAN when its received signal strength in a neighboring sector exceeds a comparative threshold level. The RAN may then responsively instruct the WCD to switch over to communicate in that neighboring sector (e.g., to add the neighboring sector to its “active” sector list).
As a general matter, WCDs can be characterized as either “mobile” or “fixed” wireless devices. A core distinction between these types is that mobile wireless devices can and do generally move from place to place, whereas fixed wireless devices usually remain at a known, fixed position. By way of example, mobile wireless devices may include handheld cell phones, wirelessly-equipped PDAs (or handheld computers), and the like, which a user would typically carry from place to place, whereas fixed wireless devices may include wall mounted cell phones, wirelessly-equipped desktop computers, wireless local loop (WLL) devices that provide cellular wireless connectivity for a wired telephone system, and the like, which sit in a given position.
Notwithstanding these differences, however, both mobile and fixed wireless devices typically operate in the same manner as each other with respect to the air interface and RAN. For instance, both types of devices may register with a RAN and then place and receive calls via the RAN. Further, both types of devices may engage in calls that are handed off or transferred from one wireless coverage area to another.